The fire-breating Cayman GT4 proved to be quite a hit with Porsche fanatics as the last-generation model is already sold out. Powered by a 3.8-liter flat-six borrowed from the 911 Carrera S and helped along by uprated brakes and a lower ride height, the GT4 was essentially a souped-up version of the fastback coupe.

Now it looks like Porsche is busy developing the next-gen Cayman GT4. Recently, our eagle-eyed spies were able to spot what appeared to be a test mule of the aforementioned vehicle. Based on the picutres provided, it looks like the test mule is a heavily modified 918 Boxster / Cayman with prototype exterior body panels.

Also worth noting are the unusually flared wheel arches. According to our spies, all four corners are filled with foam which could indicate Porsche is testing a new suspension system for the Cayman GT4 prototype. The exhaust also appears to be new as our spies noticed that it does not fit properly on the car. Other features installed on the test mule include a more aggressive front bumper, rear wing and sleek rear bumper.

The engine itself also remains to be a mystery but Andreas Preuniger, head of Porsche GT models, said that the new GT4 will still have a naturally-aspirated engine. This could mean that the Cayman GT4 will be driven by a de-tuned version of the 4.0-liter flat-six derived from the recently refreshed 911 GT3. Since the previous Cayman GT4 produced 385 PS and 419 Nm of torque, it's safe to say that the next-gen GT4 could produce more than 400 PS but not more than the updated GT3's 500 PS.

Other details about the next-gen Cayman GT4 test mule are still kept under wraps but there is also speculation that there will be an even more powerful variant in the form of the GT4 RS. Only time will tell whether Porsche is indeed serious in making a souped version of the GT4.